Just a comment, wreckit might disagree, in which case I bow to him.
When my installer put my system in, I indicated I might want to add a load at some point. Either a garage heater, or a greenhouse heater. He put in a pair of Tees where the 1 1/4"CB Thermopex enters the house; those Tees feed the TV for the house on one side, and a pair of valves on the other(capped, obviously). When I want to add a load, he advised that I then plumb the load in on those Tees, and put a TV at the target end of those pipes, followed by a water-air heat exchanger in a blower unit; that way, the water circulates continuously, and a thermostat would control demand in the garage. He really, really, really wanted to keep the house heat separate from the garage. Not sure if this will work for you, but I'm glad I asked when he was doing the work.
smithbr